Ahkello Witherspoon stretched with his teammates before practice on Thursday and went to the side field when football drills began.

Afterwards, the team announced the promising rookie cornerback didn’t participate in the session because of an ankle injury. His status will be updated when Kyle Shanahan addresses the media Friday afternoon ahead of Sunday’s trip to play the Chicago Bears (3-8).

Cornerback is one of San Francisco’s thinnest positions. The team traded away a prominent member of the rotation when Rashard Robinson was sent to the Jets at the trade deadline. Aside from starter Dontae Johnson, the remaining corners available are veteran Leon Hall and Greg Mabin, who were both acquired off the street midseason.

Witherspoon figures to be a key piece of the rebuilding secondary. He played well enough in practice while being inactive for games early in the season to make Robinson expendable. Getting playing time to finish off the season will be valuable for his development.

The injury didn’t appear significant, but the team might be cautious given the notoriously poor playing surface at Soldier Field.

-Rookie quarterback C.J. Beathard practiced after missing Wednesday’s session. He indicated Wednesday he’s confident about being available to back up Jimmy Garoppolo on Sunday after leaving the loss to the Seahawks with a left knee and hip injury.

-Right tackle Trent Brown was listed as limited for the second straight day. He was sporting a new shoulder harness on the right side of his shoulder pads.

-Nose tackle Earl Mitchell also missed Thursday’s practice. The team said he was given a veteran’s day off.